In enhanced Universal Terrestrial Radio Access Network (E-UTRAN), connected mode provides a user equipment assisted, network controlled handover. For example, the network may configure the user equipment with a measurement configuration, and, based on the configuration, the user equipment may then perform measurements and report those measurements to the network. The network may, based on the measurement report, command the user equipment to change cells to a target cell.
E-UTRAN also supports radio resource control (RRC) connected mode discontinuous reception mode (hereinafter referred to as DRX and/or connected mode DRX). Connected mode DRX may enable improved user equipment power saving opportunities for user equipment by allowing the user equipment to enter an inactive state (for example, switch off its receiver) for a certain period of time before it has to become active to listen to a control channel to determine whether there is a scheduled data transmission for the user equipment. When the network configures the user equipment with DRX, the network may define the value of an inactivity timer for the DRX. This DRX inactivity timer is restarted whenever a new data block is sent, but if data is not sent, the inactivity DRX timer may expire, triggering the user equipment to apply DRX. DRX is described in 3GPPP TS 36.321, V11.1.0 (2012-12), 3rd Generation Partnership Project, Technical Specification Group Radio Access Network, Evolved Universal Terrestrial Radio Access (E-UTRA), Medium Access Control (MAC) protocol specification (Release 11), Jan. 2, 2013, hereinafter TS 36.321.
DRX enables a user equipment, such as for example a smart phone and the like, to stay in connected mode for longer periods of time even though the user equipment does not have an ongoing continuous data transmission. Specifically, the user equipment may apply DRX between actual data transmissions to facilitate power savings during these inactive data transmission periods. Moreover, the use of DRX may enable user equipment power saving, without the network having to push the user equipment to an idle mode, as the user equipment can enter DRX based on the DRX inactivity timer noted above.
Although DRX enables power saving, DRX may introduce a mobility challenge as the user equipment is not required to perform as many measurements in DRX mode when compared to non-DRX mode (for example, during an active data transmission session), especially for long DRX periods of about 640 milliseconds and above, for high velocity user equipment, and smaller cells of a heterogeneous network.
The expected increase in wireless data transmissions may mean that there will be a need to deploy more network capacity. One efficient way to increase the network capacity is by deploying small cells for offloading purposes or offloading cells in general. These small cells can be deployed on the same or separate carriers relative to the serving cell, and the mixed environment with macro/large cells and small cells are often referred to heterogeneous networks (hetnets). Use of hetnets may provide opportunities for offloading traffic from the macrocells to a typically higher speed or capacity small cell.
The heterogeneous network may include one or more wireless access points, or base stations, such as for example an E-UTRAN (evolved Universal Mobile Telecommunications System Terrestrial Radio Access Network) NodeB base station serving macrocells, and one or more small cell base stations serving small cells. For example, a small cell base station (or a wireless access point or a remote radio head) may be implemented to cover a small cell, or coverage area, examples of which include a residence, a small business, a building, an office, or a small area. As such, the small cell base station, such as for example a home base station (HNB), a home E-UTRAN NodeB base station (HeNB), a WiFi access point, and the like, may be configured to have functionality similar to a typical base station, such as for example an E-UTRAN NodeB (eNB) base station, but the small cell base station may have less/smaller coverage/range and lower power capabilities given its limited coverage area or class. For example, the small cell base station may be implemented as a femtocell wireless access point/base station having power sufficient for a cell serving wireless devices within a limited range of about tens of meters. Picocell base stations are another example of a small cell base station, but picocell base stations have somewhat greater range serving a small area on the order of about 100-200 meters. Accordingly, wireless service providers view small cell base stations as a way to extend service coverage into a small cell, as a way to offload traffic to the small cell base stations, and/or as a way to provide enhanced service, such as for example higher data rates, lower latencies, energy efficiency and the like, within the small cell, when compared to the larger macrocell served by a typical base station, such as for example the eNB base station.